/**
 * Copyright 2010 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
package net.oauth.jsontoken.crypto;

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.PublicKey;
import java.security.Signature;
import java.security.SignatureException;

/**
 * A verifier that can verify signatures on byte arrays using RSA and SHA-256.
 */
public class RsaSHA256Verifier implements Verifier {

    private final PublicKey verificationKey;
    private final Signature signer;

    /**
     * Public Constructor.
     * @param verificationKey the key used to verify the signature.
     */
    public RsaSHA256Verifier(PublicKey verificationKey) {
        this.verificationKey = verificationKey;
        try {
            this.signer = Signature.getInstance("SHA256withRSA");
            this.signer.initVerify(verificationKey);
        }
        catch (NoSuchAlgorithmException e) {
            throw new IllegalStateException("platform is missing RSAwithSHA256 signature alg", e);
        }
        catch (InvalidKeyException e) {
            throw new IllegalStateException("key is invalid", e);
        }
    }

    /*
     * (non-Javadoc)
     * @see net.oauth.jsontoken.crypto.Verifier#verifySignature(byte[], byte[])
     */
    @Override
    public void verifySignature(byte[] source, byte[] signature) throws SignatureException {
        try {
            signer.initVerify(verificationKey);
        }
        catch (InvalidKeyException e) {
            throw new RuntimeException("key someone become invalid since calling the constructor");
        }
        signer.update(source);
        if (!signer.verify(signature)) {
            throw new SignatureException("signature did not verify");
        }
    }
}
